Method for focusing miniature ultrasound transducers

ABSTRACT

The present disclosure provides methods and apparatus of fabricating a transducer for use in ultrasound imaging. A substrate is provided. The substrate may be a silicon substrate having a first side and a second side opposite the first side. A transducer membrane is formed over the first side of the substrate. The transducer membrane includes a piezoelectric component. A well is formed in the substrate from the second side. A backing material is dispensed onto a first sidewall of the well in a manner so as to create a capillary effect that causes the backing material to wick down the sidewall, across the back side of the substrate exposed by the well, and up a second sidewall of the well. The transducer membrane is deflected so that the transducer membrane has a concave shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Patent Application No.61/745,212, filed Dec. 21, 2012, and entitled “Method and Apparatus forFocusing Miniature Ultrasound Transducers,” the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to ultrasound imaging, and inparticular, to a miniature ultrasound transducer, such as apiezoelectric micromachined ultrasound transducer (PMUT), used forintravascular imaging.

BACKGROUND

Intravascular ultrasound (IVUS) imaging is widely used in interventionalcardiology as a diagnostic tool for assessing a vessel, such as anartery, within the human body to determine the need for treatment, toguide intervention, and/or to assess its effectiveness. An IVUS imagingsystem uses ultrasound echoes to form a cross-sectional image of thevessel of interest. Typically, IVUS imaging uses a transducer on an IVUScatheter that both emits ultrasound signals (waves) and receives thereflected ultrasound signals. The emitted ultrasound signals (oftenreferred to as ultrasound pulses) pass easily through most tissues andblood, but they are partially reflected by discontinuities arising fromtissue structures (such as the various layers of the vessel wall), redblood cells, and other features of interest. The IVUS imaging system,which is connected to the IVUS catheter by way of a patient interfacemodule, processes the received ultrasound signals (often referred to asultrasound echoes) to produce a cross-sectional image of the vesselwhere the IVUS catheter is located.

IVUS catheters typically employ one or more transducers to transmitultrasound signals and receive reflected ultrasound signals. However,conventional methods and apparatuses for fabricating transducers may notbe optimized. For example, conventional methods and apparatuses do notdisclose how to shape a thin polymer film into an ultrasound transducerhaving concave, lens-like geometries in an automated process.

Therefore, while conventional methods and apparatuses of fabricatingtransducers are generally adequate for their intended purposes, theyhave not been entirely satisfactory in every aspect.

SUMMARY

Ultrasound transducers are used in intravascular ultrasound (IVUS)imaging to assess medical conditions inside a human body. According tothe present disclosure, the fabrication of ultrasound transducersinvolves shaping a thin polymer film into a concave, lens-liketransducer membrane. The polymer film may have piezoelectric properties,which means that electrical charge may be acquired when the polymer filmis compressed, twisted, or otherwise distorted. The polymer film isformed over a front side of a substrate. A well is formed from the backside of the substrate. A backing material, such as epoxy, is dispensedinto the well. The polymer film is then deflected into having a concaveshape.

One aspect of the present disclosure involves a method of fabricating aminiature ultrasound transducer. The method includes: providing asubstrate having a first side and a second side opposite the first side;forming a transducer membrane over the first side of the substrate, thetransducer membrane including a piezoelectric component; forming a wellin the substrate from the second side; dispensing a backing materialonto a first sidewall of the well in a manner so as to create acapillary effect that causes the backing material to wick down thesidewall, across the back side of the substrate exposed by the well, andup a second sidewall of the well; and deflecting the transducer membraneso that the transducer membrane has a concave shape.

Another aspect of the present disclosure involves a method offabricating an ultrasound transducer. The method includes: providing awafer having a first side and a second side opposite the first side;forming a transducer membrane over the first side of the wafer, thetransducer membrane including a piezoelectric component; forming anopening in the wafer from the second side; partially filling the openingwith an epoxy material in a manner such that a predetermined amount ofhead space is reserved in the well; applying air pressure to thetransducer membrane from the first side to deflect a portion of thetransducer membrane towards the second side; and curing the epoxymaterial by heat during the applying the air pressure.

Yet another aspect of the present disclosure involves: a method ofshaping a transducer. The method includes: providing a wafer having afirst side and a second side opposite the first side; forming amulti-layered transducer membrane over the first side of the wafer, oneof the layers of the transducer membrane being a piezoelectric layer;forming a well in the wafer, the well being open to the second side;dispensing an epoxy material into a sidewall of the well in a manner soas to induce a capillary effect that causes the well to be partiallyfilled substantially without air bubbles; deflecting the transducermembrane by applying pressurized air from the first side until thetransducer membrane achieves an arcuate shape; and curing the epoxymaterial while the transducer membrane is deflected.

Another aspect of the present disclosure involves a transducer shapingchamber for shaping ultrasound transducers. The transducer shapingchamber includes: a transducer coupon carrier having one or more slots,the one or more slots each being geometrically shaped to hold atransducer coupon having a plurality of ultrasound transducers formedthereon; a first plate disposed over a first side of the transducercoupon carrier; and a second plate disposed over a second side of thetransducer coupon carrier, the second side being opposite the firstside; wherein the transducer shaping chamber is configured to move thefirst plate and the second plate toward each other so as to push againstthe transducer coupon carrier from the first and second sides,respectively, until the transducer coupon carrier has been sealedagainst the first plate and with the second plate.

One more aspect of the present disclosure involves a system forfabricating an ultrasound transducer. The system includes: a controlpanel that includes a plurality of control mechanisms configured to seta plurality of fabrication process parameters, the fabrication processparameters being selected from the group consisting of: processpressure, process time, process duration, and process voltage; and atransducer shaping chamber communicatively coupled to the control paneland configured to implement the fabrication process parameters thereinin response to instructions from the control panel, the transducershaping chamber including: a removable part carrier configured to load atransducer coupon having a plurality of transducers formed thereon, thetransducers each having a transducer membrane disposed over a wellpartially filled with an epoxy; a first plate configured to support andseal against the part carrier from a first side, the first plate facingthe transducer well; and a second plate configured to support and sealagainst the part carrier from a second side opposite the first side, thesecond plate facing toward the transducer membrane; wherein: the firstand second plates are configured to be moved toward each other until thepart carrier is sealed between the first plate and the second plate; andthe transducer shaping chamber is configured to deflect the transducermembrane into an arcuate shape through application of pressurized air.

Another aspect of the present disclosure involves a transducer shapingapparatus for shaping a plurality of ultrasound transducerscollectively. The apparatus includes: a bottom plate having an air holethat allows a pressurized air to be delivered into the transducershaping apparatus; a removable transducer coupon carrier disposed overthe bottom plate, the transducer coupon carrier including a slot that isgeometrically configured to hold and support a transducer coupon havinga plurality of ultrasound transducers formed thereon, and wherein theslot includes an air inlet coupled to the air hole of the bottom plate,the air inlet allowing the pressurized air to be applied to theplurality of transducers collectively; a top plate disposed over thetransducer coupon carrier, the top plate being configured to be heated;and wherein the top plate and the bottom plate are configured to bemoved toward each other so as to seal against the transducer couponcarrier from opposites sides and seal the transducer coupon carriertherebetween while the pressurized air is applied to the plurality oftransducers.

Both the foregoing general description and the following detaileddescription are exemplary and explanatory in nature and are intended toprovide an understanding of the present disclosure without limiting thescope of the present disclosure. In that regard, additional aspects,features, and advantages of the present disclosure will become apparentto one skilled in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. In addition, the present disclosuremay repeat reference numerals and/or letters in the various examples.This repetition is for the purpose of simplicity and clarity and doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

FIG. 1 is a schematic illustration of an intravascular ultrasound (IVUS)imaging system according to various aspects of the present disclosure.

FIGS. 2-3, 5-6 and 14 are diagrammatic cross-sectional side views of anultrasound transducer at different stages of fabrication according tovarious aspects of the present disclosure.

FIG. 4 is a diagrammatic illustration of how a backing material isdispensed into a well of the ultrasound transducer according to variousaspects of the present disclosure.

FIGS. 7-13 are block diagrams and illustrations of a transducer shapingsystem according to various aspects of the present disclosure.

FIG. 15 is a flowchart illustrating a method for fabricating anultrasound transducer according to various aspects of the presentdisclosure.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. For example, the present disclosure provides an ultrasoundimaging system described in terms of cardiovascular imaging, however, itis understood that such description is not intended to be limited tothis application, and that such imaging system can be utilized forimaging throughout the body. In some embodiments, the illustratedultrasound imaging system is a side looking intravascular imagingsystem, although transducers formed according to the present disclosurecan be mounted in other orientations including forward looking. Theimaging system is equally well suited to any application requiringimaging within a small cavity. In particular, it is fully contemplatedthat the features, components, and/or steps described with respect toone embodiment may be combined with the features, components, and/orsteps described with respect to other embodiments of the presentdisclosure. For the sake of brevity, however, the numerous iterations ofthese combinations will not be described separately.

There are primarily two types of catheters in common use today:solid-state and rotational. An exemplary solid-state catheter uses anarray of transducers (typically 64) distributed around a circumferenceof the catheter and connected to an electronic multiplexer circuit. Themultiplexer circuit selects transducers from the array for transmittingultrasound signals and receiving reflected ultrasound signals. Bystepping through a sequence of transmit-receive transducer pairs, thesolid-state catheter can synthesize the effect of a mechanically scannedtransducer element, but without moving parts. Since there is no rotatingmechanical element, the transducer array can be placed in direct contactwith blood and vessel tissue with minimal risk of vessel trauma, and thesolid-state scanner can be wired directly to the imaging system with asimple electrical cable and a standard detachable electrical connector.

An exemplary rotational catheter includes a single transducer located ata tip of a flexible driveshaft that spins inside a sheath inserted intothe vessel of interest. The transducer is typically oriented such thatthe ultrasound signals propagate generally perpendicular to an axis ofthe catheter. In the typical rotational catheter, a fluid-filled (e.g.,saline-filled) sheath protects the vessel tissue from the spinningtransducer and driveshaft while permitting ultrasound signals to freelypropagate from the transducer into the tissue and back. As thedriveshaft rotates (for example, at 30 revolutions per second), thetransducer is periodically excited with a high voltage pulse to emit ashort burst of ultrasound. The ultrasound signals are emitted from thetransducer, through the fluid-filled sheath and sheath wall, in adirection generally perpendicular to an axis of rotation of thedriveshaft. The same transducer then listens for returning ultrasoundsignals reflected from various tissue structures, and the imaging systemassembles a two dimensional image of the vessel cross-section from asequence of several hundred of these ultrasound pulse/echo acquisitionsequences occurring during a single revolution of the transducer.

FIG. 1 is a schematic illustration of an ultrasound imaging system 100according to various aspects of the present disclosure. In someembodiments, the ultrasound imaging system 100 includes an intravascularultrasound imaging system (IVUS). The IVUS imaging system 100 includesan IVUS catheter 102 coupled by a patient interface module (PIM) 104 toan IVUS control system 106. The control system 106 is coupled to amonitor 108 that displays an IVUS image (such as an image generated bythe IVUS system 100).

In some embodiments, the IVUS catheter 102 is a rotational IVUScatheter, which may be similar to a Revolution® Rotational IVUS ImagingCatheter available from Volcano Corporation and/or rotational IVUScatheters disclosed in U.S. Pat. No. 5,243,988 and U.S. Pat. No.5,546,948, both of which are incorporated herein by reference in theirentirety. The catheter 102 includes an elongated, flexible cathetersheath 110 (having a proximal end portion 114 and a distal end portion116) shaped and configured for insertion into a lumen of a blood vessel(not shown). A longitudinal axis LA of the catheter 102 extends betweenthe proximal end portion 114 and the distal end portion 116. Thecatheter 102 is flexible such that it can adapt to the curvature of theblood vessel during use. In that regard, the curved configurationillustrated in FIG. 1 is for exemplary purposes and in no way limits themanner in which the catheter 102 may curve in other embodiments.Generally, the catheter 102 may be configured to take on any desiredstraight or arcuate profile when in use.

A rotating imaging core 112 extends within the sheath 110. The imagingcore 112 has a proximal end portion 118 disposed within the proximal endportion 114 of the sheath 110 and a distal end portion 120 disposedwithin the distal end portion 116 of the sheath 110. The distal endportion 116 of the sheath 110 and the distal end portion 120 of theimaging core 112 are inserted into the vessel of interest duringoperation of the IVUS imaging system 100. The usable length of thecatheter 102 (for example, the portion that can be inserted into apatient, specifically the vessel of interest) can be any suitable lengthand can be varied depending upon the application. The proximal endportion 114 of the sheath 110 and the proximal end portion 118 of theimaging core 112 are connected to the interface module 104. The proximalend portions 114, 118 are fitted with a catheter hub 124 that isremovably connected to the interface module 104. The catheter hub 124facilitates and supports a rotational interface that provides electricaland mechanical coupling between the catheter 102 and the interfacemodule 104.

The distal end portion 120 of the imaging core 112 includes a transducerassembly 122. The transducer assembly 122 is configured to be rotated(either by use of a motor or other rotary device or manually by hand) toobtain images of the vessel. The transducer assembly 122 can be of anysuitable type for visualizing a vessel and, in particular, a stenosis ina vessel. In the depicted embodiment, the transducer assembly 122includes a piezoelectric micromachined ultrasonic transducer (“PMUT”)transducer and associated circuitry, such as an application-specificintegrated circuit (ASIC). An exemplary PMUT used in IVUS catheters mayinclude a polymer piezoelectric membrane, such as that disclosed in U.S.Pat. No. 6,641,540, hereby incorporated by reference in its entirety.The PMUT transducer can provide greater than 100% bandwidth for optimumresolution in a radial direction, and a spherically-focused aperture foroptimum azimuthal and elevation resolution.

The transducer assembly 122 may also include a housing having the PMUTtransducer and associated circuitry disposed therein, where the housinghas an opening that ultrasound signals generated by the PMUT transducertravel through. In yet another alternative embodiment, the transducerassembly 122 includes an ultrasound transducer array (for example,arrays having 16, 32, 64, or 128 elements are utilized in someembodiments).

The rotation of the imaging core 112 within the sheath 110 is controlledby the interface module 104, which provides user interface controls thatcan be manipulated by a user. The interface module 104 can receive,analyze, and/or display information received through the imaging core112. It will be appreciated that any suitable functionality, controls,information processing and analysis, and display can be incorporatedinto the interface module 104. In an example, the interface module 104receives data corresponding to ultrasound signals (echoes) detected bythe imaging core 112 and forwards the received echo data to the controlsystem 106. In an example, the interface module 104 performs preliminaryprocessing of the echo data prior to transmitting the echo data to thecontrol system 106. The interface module 104 may perform amplification,filtering, and/or aggregating of the echo data. The interface module 104can also supply high- and low-voltage DC power to support operation ofthe catheter 102 including the circuitry within the transducer assembly122.

In some embodiments, wires associated with the IVUS imaging system 100extend from the control system 106 to the interface module 104 such thatsignals from the control system 106 can be communicated to the interfacemodule 104 and/or visa versa. In some embodiments, the control system106 communicates wirelessly with the interface module 104. Similarly, itis understood that, in some embodiments, wires associated with the IVUSimaging system 100 extend from the control system 106 to the monitor 108such that signals from the control system 106 can be communicated to themonitor 108 and/or vice versa. In some embodiments, the control system106 communicates wirelessly with the monitor 108.

FIGS. 2-3, 4-5, and 11 are diagrammatic fragmentary cross-sectional sideviews of a miniature ultrasound transducer 200 at different stages offabrication in accordance with various aspects of the presentdisclosure. FIGS. 2-3, 4-5, and 11 have been simplified for the sake ofclarity to better understand the inventive concepts of the presentdisclosure.

The ultrasound transducer 200 can be included in the IVUS imaging system100 of FIG. 1, for example in the transducer assembly 122. Theultrasonic transducer 200 has a small size and achieves a highresolution, so that it is well suited for intravascular imaging. In someembodiments, the ultrasonic transducer 200 has a size on the order oftens or hundreds of microns, can operate in a frequency range betweenabout 1 mega-Hertz (MHz) to about 135 MHz, and can provide sub 50 micronresolution while providing depth penetration of at least 10 millimeters(mm). Furthermore, the ultrasonic transducer 200 is also shaped in amanner to allow a developer to define a target focus area based on adeflection depth of a transducer aperture, thereby generating an imagethat is useful for defining vessel morphology, beyond the surfacecharacteristics. The various aspects of the ultrasound transducer 200and its fabrication are discussed in greater detail below.

In the depicted embodiment, the ultrasound transducer 200 is apiezoelectric micromachined ultrasound transducer (PMUT). In otherembodiments, the transducer 200 may include an alternative type oftransducer. Additional features can be added in the ultrasoundtransducer 200, and some of the features described below can be replacedor eliminated for additional embodiments of the ultrasound transducer200.

Referring now to FIG. 2, the transducer 200 includes a substrate 210(also referred to as a wafer). The substrate 210 has a surface 212 and asurface 214 that is opposite the surface 212. The surface 212 may alsobe referred to as a front surface or a front side, and the surface 214may also be referred to as a back surface or a back side. In thedepicted embodiment, the substrate 210 is a siliconmicroelectromechanical system (MEMS) substrate. The substrate 210includes another suitable material depending on design requirements ofthe PMUT transducer 200 in alternative embodiments.

The substrate 210 may also include various layers that are notseparately depicted and that can combine to form electronic circuitry,which may include various microelectronic elements. Thesemicroelectronic elements may include: transistors (for example, metaloxide semiconductor field effect transistors (MOSFET), complementarymetal oxide semiconductor (CMOS) transistors, bipolar junctiontransistors (BJT), high voltage transistors, high frequency transistors,p-channel and/or n-channel field effect transistors (PFETs/NFETs));resistors; diodes; capacitors; inductors; fuses; and/or other suitableelements. The various layers may include high-k dielectric layers, gatelayers, hard mask layers, interfacial layers, capping layers,diffusion/barrier layers, dielectric layers, conductive layers, othersuitable layers, or combinations thereof. The microelectronic elementscould be interconnected to one another to form a portion of anintegrated circuit, such as a logic device, memory device (for example,a static random access memory (SRAM)), radio frequency (RF) device,input/output (I/O) device, system-on-chip (SoC) device, other suitabletypes of devices, or combinations thereof.

A thickness 220 of the substrate 210 is measured between the surface 212and the surface 214. In some embodiments, the thickness 220 is in arange from about 100 microns (um) to about 600 um. In the illustratedembodiment, the substrate 210 is a part of a wafer that includes aplurality of mass-produced miniature transducers. These miniaturetransducers are substantially similar to the transducer 200 and aresimultaneously fabricated with the transducer 200 using the samefabrication processes discussed herein. For the sake of simplicity, onlyone of these miniature transducers 200 is described in detail below, butit is understood that the same discussions apply to the other miniaturetransducers on the wafer as well.

Referring now to FIG. 3, a transducer membrane 360 is formed over thefront surface 212 of the substrate 210. The transducer membrane 360includes a polymer material, for example a piezoelectric polymermaterial. In various embodiments, the piezoelectric material may includepolyvinylidene fluoride (PVDF) or its co-polymers, polyvinylidenefluoride-trifluoroethylene (PVDF-TrFE), or polyvinylidenefluoride-tetrafluoroethylene (PVDF-TFE). Alternatively, polymers such asPVDF-CTFE or PVDF-CFE may be used.

In some embodiments, the polymer material of the transducer membrane 360is formed to have a high β phase crystallinity. β phase crystallinity isimportant when using PVDF-TrFE in piezoelectric applications, as the βphase crystallinity is a crystalline phase that is capable of retainingpermanent polarization, which is needed for a semi crystalline polymerto become piezoelectric. A method to form a polymer film with high βphase crystallinity using a coating process (such as spin coating) isdescribed in Provisional U.S. Patent Application 61/745,091 to Dylan VanHoven, filed on December 21, entitled “Preparation and Application of aPiezoelectric Film for an Ultrasound Transducer”, the contents of whichare herein incorporated by reference in its entirety.

In addition to the polymer material (e.g., the PVDF-TrFE material), thetransducer membrane 360 may also include conductive layers that provideelectrical access to the transducer membrane 360. These conductivelayers may have a metal composition and may be formed on either side(i.e., top and bottom sides) of the polymer material, such that at leasta portion of the polymer material is sandwiched between the conductivelayers. In various embodiments, the conductive layers are formed throughone or more deposition processes (e.g., chemical vapor deposition (CVD),physical vapor deposition (PVD), atomic layer deposition (ALD), orcombinations thereof) followed by one or more lithography patterningprocesses. In some embodiments, the transducer membrane may furtherinclude a dielectric support layer (e.g., an oxide layer). The variouslayers of the transducer membrane 360 and the fabrication thereof aredescribed in more detail in Provisional U.S. Patent Application61/740,998 to Cheryl R. Rice, filed on December 21, entitled “Method ofFabricating the MEM's FACT Transducer”, the contents of which are hereinincorporated by reference in its entirety. For reasons of simplicity,the structural details of the transducer membrane are not specificallyshown herein.

Pad metals 370-371 may also be formed over the surface 212 of thesubstrate 210. The pad metals 370-371 may be formed by depositing alayer of metal over the substrate 210 and thereafter patterning thelayer of metal in a lithography process. The pad metals 370-371 are eachelectrically coupled to a respective one of the conductive layers of thetransducer membrane 360. As such, the pad metals 370-371 may serve aselectrodes for the transducer 200, so that electrical connections may beestablished between the transducer 200 and external devices such aselectronic circuitry (not illustrated herein). The electronic circuitrycan excite the transducer membrane 360 so that it generates sound waves,particularly sound waves in an ultrasound range.

A well 380 is formed in the substrate 210 from the back side 214. Thewell 380 may also be referred to as an opening, a void, or a recess. Insome embodiments, the well 380 is formed up to the bottom surface of thetransducer membrane 360. In other words, a portion of the transducermembrane 360 is exposed by the well 380. In some embodiments, the well380 is formed by an etching process, for example a deep reactive ionetching (DRIE) process. The well 380 forms an aperture of the transducer200. Thereafter, the surface around the individual transducer 200 may beetched to define a singulated form factor for the device.

The well 380 is then filled with an epoxy material to dampen soundcoming off the back side of the transducer 200 and to also permanentlyhold the transducer membrane 360 into a lens-like shape. In someembodiments, the epoxy material is dispensed into the well 380 manually.In other embodiment, the epoxy material is dispensed into the well 380automatically via an x, y, z automated stage. For example, in someembodiments, the D-583 or D-585 DispenseMate Benchtop Dispensing Systemsfrom Nordson Asymtek may be used. These dispensing systems may implementa closed-loop DC servo motion control and/or a Jet-on-the-fly jetdispensing capability, as well as software for intuitive userprogramming. In some cases, these dispensing systems may have integratedheight sensors and/or digital gauges for easy setup and greaterprogramming accuracy.

FIG. 4 is a simplified diagrammatic illustration of how the epoxymaterial is dispensed into the well 380. It is understood that the well380 illustrated in FIG. 4 is flipped upside-down (from FIG. 3), suchthat the side 212 in FIG. 3 is located near the bottom of FIG. 4, andthe side 214 in FIG. 3 is located near the top of FIG. 4. As discussedabove, the transducer 200 herein is a miniature transducer whose smalldimensions may make its well 380 difficult to fill. For example,conventional processes used to fill such wells as small as the well 380may lead to air bubbles being trapped in the well, thereby degrading thewell's performance. To overcome these problems, the present disclosureinvolves a novel well-filling process (discussed below in more detail)that utilizes a capillary effect to ensure the well 380 is filledwithout the problems associated with conventional methods.

In some embodiments, a dispenser 390 is used to dispense a liquid epoxymaterial 400 into the well 380. The dispenser 390 may be a needle or asyringe in certain embodiments. In some embodiments, the epoxy material400 has a viscosity in a range from about 1 cP to about 10,000 cP. Asshown in FIG. 4, the epoxy material 400 is dispensed onto a sidewall380A of the well 380. The difference in surface energies between thesubstrate 210 and the epoxy material 400 causes a capillary effect. Dueto the capillary effect, the epoxy material 400 wicks down the sidewall380A of the well 380, across the back surface of the transducer, andthen up the other sidewall 380C of the well 380. The dispenser 390dispenses the epoxy material 400 in this manner until the epoxy materialalmost completely fills the entire well 380.

In the illustrated embodiments, an operator can control the dispensepressure and dispense time. Dispense pressure is dependent on the epoxyviscosity and the size of the dispenser 390. A dispensing speed may ormay not be measured, but it is dependent on the size of the well 380 andthe dispensing pressure. Once a suitable pressure is found, dispensetime is manipulated to control the amount of epoxy dispensed into thewell 380. The placement (i.e. on the side of the well 380) of thedispenser and the amount of epoxy 400 dispensed thereinto are carefullycontrolled. A sufficient amount of epoxy 400 should be dispensed intothe well 380 so that when the wafer is thinned later, the well 380 isfull with epoxy. On the other hand, the amount of epoxy dispensed shouldnot completely fill the well 380 prior to wafer thinning/back grinding,because the transducer film (discussed below) will not have anywhere togo when shaping pressure is applied to the face of it, which means thetransducer film will not be capable of being shaped like a lens.

To induce or facilitate the capillary effect discussed above, someadditional measures may be taken in various embodiments. For instance, atip 390A of the dispenser 390 may be positioned sufficiently adjacent tothe sidewall 380A. In some embodiments, the tip 390A of the dispenser390 is in physical contact with the sidewall 380A. In other embodiments,the tip 390A and the sidewall 380A are positioned sufficiently close sothat the epoxy 400 is guaranteed to make contact with the sidewall 380Awhen it exits the tip 390A. The distance (if any) between the tip 390Aand the sidewall 380A may be a function of a plurality of factors,including (but not limited to) surface energy of the tip 390A, epoxy,sidewall and atmosphere (which is dependent on ambient temperature andrelative humidity), as well as capillary number of the epoxy 400. In anycase, the close proximity of the tip 390A of the dispenser and thesidewall 380A ensures that the dispensed epoxy material 400 will comeinto contact with the sidewall 380A first, rather than dripping downdirectly to a bottom 380B of the well (the bottom 380B of the well maybe the exposed back side surface of the substrate 210, for example). Insome embodiments, the vertical position of the tip 390A may also vary asthe epoxy material 400 is dispensed. For example, the tip 390A mayinitially be positioned closer to the bottom 380B of the well 380. Asthe epoxy material 400 is being dispensed into the well 380, the tip390A may be moved “up” away from the bottom 380B of the well, whilestill maintaining close proximity to the sidewall 380A.

In some embodiments, the well 380 is not 100% filled. In order words,the dispenser 390 stops dispensing the epoxy 400 before the well 380 is100% filled. This leaves some head space in the well 380, which reservesroom for the transducer membrane 360 (FIG. 3) to be shaped back into thewell 380. This scenario is graphically illustrated in FIG. 5, which is asimplified diagrammatic cross-sectional side view of the transducer 200.Once again, the transducer 200 is flipped upside-down from the viewshown in FIG. 3. As shown in FIG. 5, the dispenser 390 is used todispense the epoxy material 400 into the sidewall 380A of the well 380.The epoxy material 400 wicks down the sidewall 380A and gradually fillsthe well 380 due to the capillary effect discussed above. This processhelps prevent air bubbles in the epoxy material as it is dispensed intothe well 380.

The dispensing process ends while some head room or head space 410 inthe well is maintained. The amount of head space 410 may bepredetermined or predefined. In some embodiments, the amount of headspace 410 is dependent on a diameter of the transducer 200 and thedesired focal length of the device (which is correlated to an “Fnumber”). For example, an equation D=a/(8*F) can be used to determinethe amount of deflection (D) (at the center position of the transducermembrane) needed for a given aperture (a) and a desired F number (F)(the F number=2×the focal length). As an example, an F number of about 3mm is desired (i.e., focal length=1.5 mm), and the transducer aperturediameter is about 0.5 millimeters (mm). To achieve such F number and thetransducer aperture diameter, the deflection (D) is calculated to beabout 0.019 mm. In other words, the transducer membrane 360 needs to bedeflected by about 0.019 mm. It is also understood that some additionalhead room may be allowed to account for manufacturing tolerances. Ofcourse, it is understood that these numbers here are provided merely asexamples, and that other numerical values may be used in alternativeembodiments.

In alternative embodiments, the well 380 may be completely filled withthe epoxy material 400, which may be intentional or inadvertent. In thatcase, a squeegeeing process is performed to remove undesired excessepoxy material off the back side 214 of the substrate 210. Thesqueegeeing process is shown in FIG. 6, which is a simplifieddiagrammatic cross-sectional side view of the transducer 200. As shownin FIG. 6, the well 380 is completely filled by the epoxy material 400.This may be undesirable because now there is no room to account for the(upcoming) deflection of the transducer membrane 360. Therefore, asqueegeeing device 420 is placed on the surface 214 of the substrate210. The squeegeeing device 420 moves along the surface 214 of thesubstrate. As it passes by the epoxy material 400 in the well 380, italso creates a capillary effect. Due to the capillary effect, some ofthe epoxy material 400 is pulled out of the well 400. As such, undesiredexcess epoxy material 400 may still be removed from the well 380,thereby creating the head room 410 shown in FIG. 5. As discussed above,the amount of the head room 380 is configured to be enough to accountfor the deflection of the transducer membrane 360, which will bediscussed below in more detail.

According to the various aspects of the present disclosure, thetransducer 200 is shaped using a transducer shaping apparatus 450, anembodiment of which is shown in the simplified block diagram of FIG. 7.The transducer shaping apparatus 450 is an automated piece of equipmentin the present disclosure, which acts like an internally pressurizedheated metal press. The transducer shaping apparatus 450 includes acontrol panel 460 and a shaping chamber 461 that is communicativelycoupled with the control panel 460. The control panel 460 includesvarious control and input/output mechanisms to facilitate interactionwith a human user. The shaping chamber 461 includes various mechanicaland electrical components to carry out the actual shaping of thetransducer membrane 360 in response to instructions received from thecontrol panel 460. Diagrammatic perspective views of the control panel460 and the shaping chamber 461 are shown in FIGS. 8 and 9,respectively. The deflection operation of the transducer membrane 360 isdiscussed below in view of FIGS. 8-9 in more detail.

Referring to FIG. 8, the control panel 460 allows an operator to setprocess parameters including: cure temperature, shaping pressure,process time, and chamber closing pressure. The control panel 460 alsoallows the operator to start and stop the process via a “Start” button470, and a “Stop/Reset” button 471. The control panel 460 also includesthe following interactive mechanisms: a mechanism 472 for setting anddisplaying remaining process time, a mechanism 473 for setting anddisplaying cure temperature, a mechanism 474 for setting and displayingcurrent shaping pressure, a mechanism 475 for setting and displayingcurrent closing pressure, a mechanism 476 for setting and displayingcurrent voltage applied to the shaping pressure regulator, and amechanism 477 for setting and displaying current voltage applied to theclosing pressure regulator. The control panel 460 also includes apressure adjust mechanism 478 for adjusting pressure. In addition, thecontrol panel 460 has a process indicator button 479 for indicating aprocess is ongoing, and an alarm indicator button 480 for alerting theoperator there is an alarm. In certain embodiments, the regulatorresponds to voltage applied from 1-5 Volts (DC) in a linear manner. Oneor more 0-100 PSI regulators are also used. Therefore, 1 Voltcorresponds to 20 PSI, 2 Volts corresponds to 40 PSI, 3 Voltscorresponds to 60 PSI, etc. Resolution on the voltage indicator is 0.001volt so as to allow for fine pressure tuning.

Although not illustrated, a digital relay is implemented inside thecontrol panel 460. The digital relay controls process sequence bysending output pulses to a timer (e.g., the mechanism 472), and airpressure solenoids (inside the instrument enclosure and not visible inFIG. 8), and receiving inputs from the timer, the start and stopswitches 470-471, and a switch mounted on the backing plate (shown inFIG. 9 and discussed below) of the shaping chamber 461. When this switchis closed, it indicates that the shaping chamber 461 is closed.

Referring now to FIG. 9, the shaping chamber 461 includes a removablepart carrier 500. The part carrier 500 may have a specific geometrymachined into it for the transducer profiles being shaped. For example,in some embodiments, the part carrier 500 accommodates one or more 1″×1″coupons of transducers (also referred to as a transducer coupon). Eachtransducer coupon has a plurality of transducers on it, for example 144transducers. Since the part carrier 500 carries transducer coupons, thepart carrier 500 may also be referred to as a transducer coupon carrier.In some embodiments, the transducer 200 may be placed on the partcarrier 500 before the epoxy material 400 is dispensed into the well380. This may take place when the part carrier 500 is outside theshaping chamber 461. After the epoxy fill process is completed (andsqueegeeing if that is needed), the part carrier 500 and the transducer200 placed thereon are then transported into the shaping chamber 461.

The shaping chamber 461 includes a backing plate 501. The backing plate501 supports the well/epoxy side of the substrate 210 when underpressure. The backing plate 501 also houses a heating element 502 andconducts heat from the heating element 502 to the epoxy material 400 andthe substrate 210 of the transducer 200. In some embodiments, thebacking plate 501 is made of a thermally conductive metal material, forexample aluminum. To prevent undesired adhesion between the transducer200 and the backing plate 501 (especially as the epoxy material 400cures), the present disclosure utilizes a release agent 503 (or releasefilm). In some embodiments, the release agent 503 includes a thinfluoropolymer release film between the backing plate 501 and thesubstrate 210 of the transducer 200. The film may be as thin as 0.001inches to 0.003 inches, for example. In other embodiments, the backingplate 501 is anodized with a polytetrafluoroethylene (PTFE) agent tofacilitate the release. Of course, other fluoropolymer films such as FEPor PFA may be used as suitable release agents as well. The use of liquidagents may not be appropriate, as they are likely to transfer to thesubstrate 210 and cause contamination of the transducer 200, which wouldinhibit other downstream processes.

The shaping chamber 461 also includes an air cylinder 504 and a bottomplate 505 resting on the air cylinder 504. The air cylinder 504 pushesthe bottom plate 505 up against the backing plate 501. When a partcarrier (for example the part carrier 500) is loaded into the bottomplate 505, O-rings on the bottom plate seal against the part carrieronce the air cylinder closes the chamber. When a part 510 (e.g., thetransducer device 200) is loaded into the part carrier 500, the part 510seals against a gasket in the part carrier 500 when the air cylinder 504closes the chamber. Once the chamber closes, and the part 510, the partcarrier 500, and the bottom plate 505 are sealed against one another, asolenoid (not illustrated in FIG. 9) in the control panel 460 (FIGS.7-8) opens and pressurizes the shaping chamber. The rods and linearbearing help guide the bottom plate 505 as it travels vertically. Insome embodiments, flow restrictors are implemented in the plumbing linesto control the rate at which the air cylinder closes the chamber and therate at which the shaping chamber pressurizes.

In the present case, after the epoxy 400 has been dispensed into thewell 380 of the transducer 200, the transducer 200 is loaded as the part510 into the shaping chamber 461. Using the control panel 460, theoperator can set the various process parameters and start the process ofshaping the transducer membrane 360. As the shaping chamber 461 closesand seals, an air pressure is applied to the front side 212 of thetransducer 200. The air pressure forces the transducer membrane 360 intoa concave shape. In some embodiments, heat is applied to the back side214 of the transducer 200 while the transducer membrane is beingdeflected. The heat cures the epoxy material 400 (or expedites thecuring of the epoxy) filling the well 380. The cured epoxy material 400serves to hold the shaped transducer membrane 360 into place. It somealternative embodiments, the epoxy material 400 may be cured by heatafter the transducer membrane 360 has already achieved the arcuate shapethrough deflection. In other words, air pressure may continue to beapplied to the transducer membrane 360, so that it will hold its arcuateshape, while the heat is applied to the epoxy material 400.

The epoxy material 400 also serves to deaden sound coming off the backof the transducer. In order to do so, the backing material 400 containsan acoustically attenuative material so that it can absorb acousticenergy (in other words, sound waves) generated by the transducermembrane 360 that travels (propagates) into the ultrasound transducer200 (for example, from the transducer membrane 360 into the backingmaterial 400). Such acoustic energy includes acoustic energy that isreflected from structures and interfaces of a transducer assembly, forexample when the ultrasound transducer 200 is included in the transducerassembly 122 of FIG. 1. To adequately deaden the sound waves, thebacking material 400 may have an acoustic impedance greater than about4.5 megaRayls in some embodiments.

FIG. 10 is a diagrammatic perspective view of a portion of the shapingchamber 461A in more detail. The bottom plate 505 is shown as beingempty—no part carrier 500 is placed on the bottom plate 505. The aircylinder 504 still provides support for the bottom plate 505. Aplurality of air inlets 520 are dispersed throughout the bottom plate505. These air inlets 520 each include a sealing O-ring. The air inlets520 are also coupled to air inlet tubing 530. The tubing 530 is coupledto the air cylinder 504 to open/close the cylinder 504. Other tubing iscoupled to the bottom plate 505 and moved through the bottom plate 505,through the part carrier (not illustrated in FIG. 10), and against theface of the transducer coupon. The tubing 530 feeds to the hole insidethe air inlet 520, and the part carrier would have a corresponding hole.The part carrier would seal against the air inlets 520.

FIG. 11A illustrates a diagrammatic top view of the removable partcarrier 500. The part carrier 500 includes one or more concave slots535, one of which is shown as an example in FIG. 11A. Each slot 535 isgeometrically configured to accommodate a transducer coupon, an exampleone of which is shown in FIGS. 11A and 11B and labeled with thereference numeral 540. As discussed above, the transducer coupon 540 ismade from a part of the wafer on which a plurality of the transducers200 are fabricated. Before the transducer membrane shaping step, thewafer is sliced or diced into a plurality of transducer coupons 540.Each transducer coupon 540 includes a plurality of transducers 200, forexample 144 transducers, which are arranged in rows and columns as shownin FIGS. 11A and 11B. It is understood that FIG. 11A shows a front sideview (i.e., the side 212 in FIGS. 2-3 and 5-6) of the transducers 200,whereas FIG. 11B shows a back side view (i.e., the side 214 in FIGS. 2-3and 5-6) of the transducers 200. In other words, FIG. 11 shows thetransducer membranes 360 being exposed, whereas FIG. 11B shows the epoxy400 partially filling the wells 380. In the illustrated embodiments, theslot 535 on the part carrier 500 has a substantially square shape, sincethat is the shape of the transducer coupon 540. However, it isunderstood that the slot 535 and the transducer coupon 540 may be shapeddifferently in alternative embodiments, as long as the slot 535 isgeometrically shaped to accommodate the transducer coupon 540.

To enhance the sealing performance when the transducer membranes 360 arebeing shaped, the present disclosure utilizes a gasket 545 in each slot535 of the part carrier 500. The gasket 545 is a “ring-like” device buthas four sides as in a square. This is because the gasket 545 also isshaped to accommodate with the shape of the transducer coupon 540. Inoperation. one side of the gasket 545 presses upon the surface of thepart carrier 500 inside the slot 535, and the other side (opposite side)of the gasket 545 presses upon the transducer coupon 540. In otherwords, the front side 212 of the transducer coupon 540 will not makeactual contact with the surface of the part carrier 500, as the gasketacts as an intermediary or a buffering mechanism between the partcarrier 500 and the transducer coupon 540. This arrangement allowsbetter sealing of the transducer coupon 540 during the transducermembrane shaping process.

The part carrier 500 also has a plurality of air lets 550, one in eachof the slots 535. During the transducer membrane shaping process, airpressure may be applied to the transducer membranes 360 through the airinlet 550. The air pressure deflects the transducer membranes 360 forall the transducers 200 on the transducer coupon 540, which is a muchmore efficient way of manufacture than conventional methods wheretransducer membranes are deflected one at a time.

FIGS. 12A and 12B are diagrammatic perspective views of a portion of thetransducer shaping chamber 461. Specifically, FIGS. 12A and 12Billustrate the backing plate 501 (also referred to as top plate), theremovable part carrier 500 having a transducer coupon 540 locatedtherein, and the bottom plate 505. As is shown in FIGS. 12A and 12B, thepart carrier 500 is disposed in between the backing plate 501 (i.e., thetop plate) and the bottom plate 505. In the embodiments of the presentdisclosure, the part carrier 500 is placed on the bottom plate 505,which is a concave slot that is geometrically shaped to accommodate thepart carrier 500. The bottom plate 505 and the backing plate 501 can bemoved towards each other to create a sealing chamber, inside which thetransducer coupon 540 may be shaped by application of air pressure. Theair pressure may be applied through the air inlets 520 (also referred toas O-rings) on the bottom plate 505. The air inlets 520 are coupled tothe air inlets 550 on the part carrier 500.

To provide more clarity to the transducer membrane shaping operationdiscussed above, FIG. 13 is provided, which illustrates a diagrammaticcross-sectional view of a portion of the transducer shaping chamber 461during the transducer membrane shaping operation. As is shown in FIG.13, a transducer coupon 540 is sealed between the backing plate 501(i.e., top plate) and the gasket 545. The transducer coupon 540 and thegasket 545 are each placed inside the square-shaped slot of the partcarrier 500. The part carrier 500 is also sealed between the bottomplate 505 and the backing plate 501. The air inlet 520 (shown in FIGS.12A-12B) extending vertically through the bottom plate 505 iscommunicatively coupled with the air inlet 550 (shown in FIGS. 11A-11B)extending vertically through the part carrier 500. Thus, pressurized airmay be applied against the transducer membranes on the transducer coupon540 through the air inlets 520 and 550. It is understood that the gasket545 does not block the air flow. The cross-sectional view of the gasket545 shows one of the four “sides” or edges of the gasket 545, but anempty space is surrounded or encircled by these four sides. It isthrough such empty space that pressurized air from the inlets 520 and550 reaches the transducer membranes on the transducer coupon 540.

In accordance with certain embodiments of the present disclosure, aninternal plumbing mechanism (e.g., air tubes) 560 may be implementedwithin the part carrier 500. The plumbing mechanism 560 extendshorizontally through the part carrier 500 and is also communicativelycoupled with the air inlet 550 (that extends vertically through the partcarrier 500). In doing so, the plumbing mechanism 560 can deliverpressurized air to adjacent air inlets (not illustrated in FIG. 13). Inother words, the structural arrangement of the portion of the transducershaping chamber 461 shown in FIG. 13 may be repeated a number of times.These additional transducer coupons 540 may be placed in the other slotsof the part carrier 500, for example, and are also sealed against thebacking plate 501 through their respective gaskets 545. Air may bedelivered to these other transducer coupons 540 through the plumbingmechanism 560, which couples together two or more of the air inlets 550each aimed at a different one of the transducer coupons 540. One benefitof applying pressurized air in this manner is that more uniformed airpressure can be applied to different groups of transducer coupons 540 atthe same time, which may lead to more uniformity of the deflection ofthe transducer membranes. Another benefit of the transducer shapingchamber 461 is that the backing plate 501 may be heated, which expeditesthe curing of the epoxy material in the wells.

FIG. 14 is a diagrammatic cross-sectional side view of the transducer200 after the transducer membrane 360 has been deflected by thetransducer shaping apparatus 450 discussed above. It is understood thatthe side 214 (i.e., the back side) of the substrate 210 has already beenthinned at this point. In other words, a suitable grinding or polishingprocess may be performed to planarize the back side of the substrate 210after the transducer membrane 360 has been shaped. Any excess epoxymaterial 400 outside the well 380 will be removed during this thinningprocess, so that the epoxy material 400 will be substantially co-planarwith (or below) the back side of the substrate 210. The thinning processis performed outside the transducer shaping apparatus and with adifferent machine,

As shown in FIG. 14, a portion 360A of the transducer membrane isdefected by the air pressure from the shaping chamber 461 such that ithas an arcuate shape. The arcuate shape of the transducer membrane 360helps is spherically focus ultrasound signals emitted therefrom. Ofcourse, it is understood that the transducer shaping apparatus 450 mayshape the transducer membrane 360 to have other shaping configurationsin different embodiments, so as to achieve various other focusingcharacteristics. For example, in an alternative embodiment, thetransducer membrane 360 may have a more arcuate shape (than it does inthe embodiment shown in FIG. 14) or a more planar shape.

FIG. 15 is a flowchart of a method 600 for fabricating an ultrasoundtransducer according to various aspects of the present disclosure. Themethod 600 includes a step 610, wherein a substrate is provided. Thesubstrate has a first side and a second side opposite the first side. Insome embodiments, the substrate is a silicon substrate and may containmicroelectronic circuitry therein.

The method 600 includes a step 620, in which a transducer membrane isformed over the first side of the substrate. The transducer membraneincludes a piezoelectric component.

The method 600 includes a step 630, in which a well is formed in thesubstrate from the second side.

The method 600 includes a step 640, in which a backing material isdispensed into the well to induce a capillary effect. In more detail,the backing material is dispensed onto a first sidewall of the well. Dueto the capillary effect caused by the surface energy difference betweenthe sidewall of the well and the backing material, the backing materialwicks down the sidewall, across the back side of the substrate exposedby the well, and up a second sidewall of the well. In some embodiments,the backing material is an epoxy material.

In some embodiments, the step 640 is performed so that the well is freeof being completely filled by the backing material. In some embodiments,the step 640 is performed so that the well is completely filled by thebacking material. In that case, the method 600 may further include astep of performing a squeegeeing process to the second side of thesubstrate so as to remove excess backing material from the well throughanother capillary effect.

The method 600 includes a step 650, in which the transducer membrane isdeflected so that the transducer membrane has a concave shape. In someembodiments, the step 650 includes applying air pressure towards thetransducer membrane so that a portion of the transducer membrane isdeflected into the well. In some embodiments, the step 650 is performedat least in part using a transducer shaping chamber. The pressurizing,opening, and closing of the transducer shaping chamber are eachperformed in an automated manner.

The method 600 includes a step 660, in which the backing material iscured while the deflection of the transducer membrane is maintained. Thebacking material may be cured by heat. In some embodiments, thetransducer shaping chamber includes a backing plate configured tosupport the second side of the substrate while the transducer membraneis deflected. The backing plate may include one or more heating elementsconfigured to generate heat, so that the backing material in the wellmay be heated during the deflecting of the transducer membrane. Theheating of the backing material helps expedite the curing of the backingmaterial.

The method 600 may further include a step of applying a release agent tothe backing plate to prevent adhesion between the backing material andthe backing plate. In some embodiments, the applying the release agentincludes anodizing the backing plate with a polytetrafluoroethylene(PTFE) material. In other embodiments, the applying the release agentincludes applying a fluoropolymer release film between the backingmaterial and the backing plate.

It is understood that additional fabrication steps may be performed tocomplete the fabrication of the transducer. However, these additionalfabrication steps are not discussed herein for reasons of simplicity.

Based on the above discussions, it can be seen that the transducershaping according to the embodiments of the present disclosure offersnumerous advantages over conventional methods. Of course, it isunderstood that not all advantages are necessarily discussed herein,other embodiments may offer different advantages, and no particularadvantage is required for all embodiments.

As one example, the present disclosure involves heating the epoxymaterial to expedite the epoxy curing. As another example, thetransducer well is filled using a capillary effect, which allows theepoxy material to wick down the side of the well, across the back sideof the transducer face, and up the remaining side of the well. Thisfilling process helps prevent air bubbles in the well. The presentdisclosure reserves sufficient head space on the back side of the epoxymaterial during the epoxy dispensation into the transducer well, so thatthere is enough room to allow for the deflection of the transducermembrane. In situations where the epoxy has filled the transducer welltoo much (i.e., not enough head space), a squeegeeing process may alsobe performed to the back side of the transducer substrate to induce acapillary effect, which will pull excess epoxy out of the well, therebycreating additional head space in the well.

As yet one more example of the advantages offered by the embodiments ofthe present disclosure, a release agent may be implemented between thetransducer substrate and the backing plate of the transducer shapingchamber to prevent the epoxy from curing to the tool. As anotherexample, the transducer shaping apparatus of the present disclosure isautomated: the opening and closing of the shaping chamber is automated,as is the pressurizing of the shaping chamber. As one more example, flowrestrictors may be used in the plumbing lines to control the rate atwhich the air cylinder closes the shaping chamber and the rate at whichthe shaping chamber pressurizes. As a further example, a removable partcarrier that has a specific geometry machined into it is utilized toshape the transducer profile.

One aspect of the present disclosure involves a method of fabricating aminiature ultrasound transducer. The method includes: providing asubstrate having a first side and a second side opposite the first side;forming a transducer membrane over the first side of the substrate, thetransducer membrane including a piezoelectric component; forming a wellin the substrate from the second side; dispensing a backing materialonto a first sidewall of the well in a manner so as to create acapillary effect that causes the backing material to wick down thesidewall, across the back side of the substrate exposed by the well, andup a second sidewall of the well; and deflecting the transducer membraneso that the transducer membrane has a concave shape.

In some embodiments, the dispensing is performed so that the well isfree of being completely filled by the backing material.

In some embodiments, the dispensing is performed so that the well iscompletely filled by the backing material, and further comprising:performing a squeegeeing process to the second side of the substrate soas to remove excess backing material from the well through anothercapillary effect.

In some embodiments, the backing material includes an epoxy material.

In some embodiments, the deflecting comprises applying air pressuretowards the transducer membrane so that a portion of the transducermembrane is deflected into the well.

In some embodiments, the method further includes: heating the backingmaterial during the deflecting of the transducer membrane to cure thebacking material.

In some embodiments, the deflecting is performed at least in part usinga transducer shaping chamber, and wherein pressurizing, opening, andclosing of the transducer shaping chamber are each automated.

In some embodiments, the transducer shaping chamber includes a backingplate configured to support the second side of the substrate while thetransducer membrane is deflected, and further comprising applying arelease agent to the backing plate to prevent adhesion between thebacking material and the backing plate.

In some embodiments, the applying the release agent comprises anodizingthe backing plate with a polytetrafluoroethylene (PTFE) material.

In some embodiments, the applying the release agent comprises applying afluoropolymer release film between the backing material and the backingplate.

Another aspect of the present disclosure involves a method offabricating an ultrasound transducer. The method includes: providing awafer having a first side and a second side opposite the first side;forming a transducer membrane over the first side of the wafer, thetransducer membrane including a piezoelectric component; forming anopening in the wafer from the second side; partially filling the openingwith an epoxy material in a manner such that a predetermined amount ofhead space is reserved in the well; applying air pressure to thetransducer membrane from the first side to deflect a portion of thetransducer membrane towards the second side; and curing the epoxymaterial by heat during the applying the air pressure.

In some embodiments, the partially filling the opening is performed bydispensing the epoxy material onto a first sidewall of the opening toinduce a capillary effect that causes the epoxy material to wick downthe sidewall, across the second side of the wafer exposed by theopening, and up a second sidewall of the opening.

In some embodiments, the deflecting is performed such that thetransducer membrane achieves an arcuate shape.

In some embodiments, the applying and the curing are performed at leastin part using a transducer shaping chamber.

In some embodiments, the transducer shaping chamber is configured topressurize, open, and close in an automated manner.

In some embodiments, the transducer shaping chamber includes a backingplate configured to support the second side of the wafer during theapplying, wherein the backing plate includes heating elements configuredto provide heat to the epoxy material during the curing.

In some embodiments, the method further includes: applying anadhesion-preventing fluoropolymer release film on the backing platebefore the applying the air pressure.

In some embodiments, the backing plate is anodized with apolytetrafluoroethylene (PTFE) material.

Another aspect of the present disclosure involves a method of shaping atransducer. The method includes: providing a wafer having a first sideand a second side opposite the first side; forming a multi-layeredtransducer membrane over the first side of the wafer, one of the layersof the transducer membrane being a piezoelectric layer; forming a wellin the wafer, the well being open to the second side; dispensing anepoxy material into a sidewall of the well in a manner so as to induce acapillary effect that causes the well to be partially filledsubstantially without air bubbles; deflecting the transducer membrane byapplying pressurized air from the first side until the transducermembrane achieves an arcuate shape; and curing the epoxy material whilethe transducer membrane is deflected.

In some embodiments, the deflecting and the curing are performed insidea transducer shaping apparatus.

In some embodiments, the method further includes thinning the wafer fromthe second side after the curing of the epoxy material.

In some embodiments, the dispensing is performed such that apredetermined amount of headspace is reserved in the well.

Yet another aspect of the present disclosure involves a transducershaping chamber for shaping ultrasound transducers. The transducershaping chamber includes: a transducer coupon carrier having one or moreslots, the one or more slots each being geometrically shaped to hold atransducer coupon having a plurality of ultrasound transducers formedthereon; a first plate disposed over a first side of the transducercoupon carrier; and a second plate disposed over a second side of thetransducer coupon carrier, the second side being opposite the firstside; wherein the transducer shaping chamber is configured to move thefirst plate and the second plate toward each other so as to push againstthe transducer coupon carrier from the first and second sides,respectively, until the transducer coupon carrier has been sealedagainst the first plate and with the second plate.

In some embodiments, the transducer coupon carrier is detachable fromthe transducer shaping chamber.

In some embodiments, the transducers each have a transducer membranedisposed over a transducer well partially filled with epoxy.

In some embodiments, the transducer coupon carrier includes an air inletfacing the transducer coupon, the air inlet allowing air to be deliveredcollectively to the transducer membranes.

In some embodiments, the transducer shaping chamber is configured todeliver air to the transducer membranes so as to deflect each of thetransducer membranes into an arcuate shape.

In some embodiments, the transducer shaping chamber is configured toheat up the first plate while the air is delivered, wherein the heatedfirst plate expedites a curing of the epoxy partially filling thetransducer well.

In some embodiments, the second plate includes an air holecommunicatively coupled to the air inlet and through which the air isdelivered to the transducer shaping chamber.

In some embodiments, the transducer coupon carrier includes an internalplumbing mechanism intersecting with, and communicatively coupled to,the air inlet, the internal plumbing mechanism being configured to allowair flow therein.

In some embodiments, the transducer shaping chamber further includes oneor more gaskets disposed at least partially inside the one or more slotsof the transducer coupon carrier, the one or more gaskets beingconfigured to facilitate the sealing of the transducer coupon with thefirst plate.

Another aspect of the present disclosure involves a system forfabricating an ultrasound transducer. The system includes: a controlpanel that includes a plurality of control mechanisms configured to seta plurality of fabrication process parameters, the fabrication processparameters being selected from the group consisting of: processpressure, process time, process duration, and process voltage; and atransducer shaping chamber communicatively coupled to the control paneland configured to implement the fabrication process parameters thereinin response to instructions from the control panel, the transducershaping chamber including: a removable part carrier configured to load atransducer coupon having a plurality of transducers formed thereon, thetransducers each having a transducer membrane disposed over a wellpartially filled with an epoxy; a first plate configured to support andseal against the part carrier from a first side, the first plate facingthe transducer well; and a second plate configured to support and sealagainst the part carrier from a second side opposite the first side, thesecond plate facing toward the transducer membrane; wherein: the firstand second plates are configured to be moved toward each other until thepart carrier is sealed between the first plate and the second plate; andthe transducer shaping chamber is configured to deflect the transducermembrane into an arcuate shape through application of pressurized air.

In some embodiments, the first plate is configured to be thermallyheated.

In some embodiments, the transducer shaping chamber, in response to thefabrication process parameters set by the control panel, heats the firstplate while delivering pressurized air to the transducers on thetransducer coupon.

In some embodiments, the removable part carrier includes a plurality ofslots, and wherein each slot is geometrically configured to hold arespective transducer coupon therein.

In some embodiments, the transducer shaping chamber further comprises aplurality of gaskets, and wherein each gasket is geometricallyconfigured to be placed into a respective one of the slots.

In some embodiments, for each gasket, one side of the gasket isconfigured to seal against the removable part carrier, and an oppositeside of the gasket is configured to seal against the transducer coupon.

In some embodiments, each slot of the removable part carrier includes anair inlet configured to receive the pressurized air.

In some embodiments, the second plate includes an air hole that iscoupled to the air inlet of the removable part carrier.

In some embodiments, the removable part carrier includes an internalplumbing mechanism that is coupled to the air inlet in one or more ofthe slots.

Yet another aspect of the present disclosure involves a transducershaping apparatus for shaping a plurality of ultrasound transducerscollectively. The apparatus includes: a bottom plate having an air holethat allows a pressurized air to be delivered into the transducershaping apparatus; a removable transducer coupon carrier disposed overthe bottom plate, the transducer coupon carrier including a slot that isgeometrically configured to hold and support a transducer coupon havinga plurality of ultrasound transducers formed thereon, and wherein theslot includes an air inlet coupled to the air hole of the bottom plate,the air inlet allowing the pressurized air to be applied to theplurality of transducers collectively; a top plate disposed over thetransducer coupon carrier, the top plate being configured to be heated;and wherein the top plate and the bottom plate are configured to bemoved toward each other so as to seal against the transducer couponcarrier from opposites sides and seal the transducer coupon carriertherebetween while the pressurized air is applied to the plurality oftransducers.

In some embodiments, the transducers each have a transducer membranedisposed over a transducer well at least partially filled with a backingmaterial, and wherein the pressurized air applied to the transducermembranes causes each transducer membranes to be deflected into anarcuate shape.

In some embodiments, the transducer shaping apparatus is configured toheat up the top plate to expedite a curing of the backing material whilethe transducer membranes are being deflected by the pressurized air.

In some embodiments, the transducer coupon carrier includes an internalplumbing mechanism intersecting with, and communicatively coupled to,the air inlet, and wherein the internal plumbing mechanism is configuredto allow air flow therein.

In some embodiments, the transducer shaping apparatus further includes agasket disposed at least partially inside the slot of the transducercoupon carrier, the gasket being configured to seal against thetransducer coupon carrier and against the transducer coupon.

Persons skilled in the art will recognize that the apparatus, systems,and methods described above can be modified in various ways.Accordingly, persons of ordinary skill in the art will appreciate thatthe embodiments encompassed by the present disclosure are not limited tothe particular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

What is claimed is:
 1. A method of fabricating a miniature ultrasoundtransducer, the method comprising: providing a substrate having a firstside and a second side opposite the first side; forming a transducermembrane over the first side of the substrate, the transducer membraneincluding a piezoelectric component; forming a well in the substratefrom the second side; dispensing, using a needle or syringe, a backingmaterial onto a first sidewall of the well in a manner so as to create acapillary effect that causes the backing material to wick down thesidewall, across the back side of the transducer membrane exposed by thewell, and up a second sidewall of the well; and deflecting thetransducer membrane so that the transducer membrane has a concave shape.2. The method of claim 1, wherein the dispensing is performed so thatthe well is free of being completely filled by the backing material. 3.The method of claim 1, wherein the dispensing is performed so that thewell is completely filled by the backing material, and furthercomprising: performing a squeegeeing process to the second side of thesubstrate so as to remove excess backing material from the well throughanother capillary effect.
 4. The method of claim 1, wherein the backingmaterial includes an epoxy material.
 5. The method of claim 1, whereinthe deflecting comprises applying air pressure towards the transducermembrane so that a portion of the transducer membrane is deflected intothe well.
 6. The method of claim 1, further comprising: heating thebacking material during the deflecting of the transducer membrane tocure the backing material.
 7. The method of claim 1, wherein thedeflecting is performed at least in part using a transducer shapingchamber, and wherein pressurizing, opening, and closing of thetransducer shaping chamber are each automated.
 8. The method of claim 7,wherein the transducer shaping chamber includes a backing plateconfigured to support the second side of the substrate while thetransducer membrane is deflected, and further comprising applying arelease agent to the backing plate to prevent adhesion between thebacking material and the backing plate.
 9. The method of claim 8,wherein the applying the release agent comprises applying afluoropolymer release film between the backing material and the backingplate.
 10. A method of fabricating an ultrasound transducer, the methodcomprising: providing a wafer having a first side and a second sideopposite the first side; forming a transducer membrane over the firstside of the wafer, the transducer membrane including a piezoelectriccomponent; forming an opening in the wafer from the second side;partially filling the opening with an epoxy material in a manner suchthat a predetermined amount of head space is reserved in the well,wherein the partially filling the opening is performed by dispensing theepoxy material onto a first sidewall of the opening to induce acapillary effect that causes the epoxy material to wick down thesidewall, across the second side of the wafer exposed by the opening,and up a second sidewall of the opening; applying air pressure to thetransducer membrane from the first side to deflect a portion of thetransducer membrane towards the second side; and curing the epoxymaterial by heat during the applying the air pressure.
 11. The method ofclaim 10, wherein the deflecting is performed such that the transducermembrane achieves an arcuate shape.
 12. The method of claim 10, whereinthe applying and the curing are performed at least in part using atransducer shaping chamber.
 13. The method of claim 12, wherein thetransducer shaping chamber is configured to pressurize, open, and closein an automated manner.
 14. The method of claim 12, wherein thetransducer shaping chamber includes a backing plate configured tosupport the second side of the wafer during the applying, wherein thebacking plate includes heating elements configured to provide heat tothe epoxy material during the curing.
 15. The method of claim 14,further comprising: applying an adhesion-preventing fluoropolymerrelease film on the backing plate before the applying the air pressure.16. A method of shaping a transducer, comprising: providing a waferhaving a first side and a second side opposite the first side; forming amulti-layered transducer membrane over the first side of the wafer, oneof the layers of the transducer membrane being a piezoelectric layer;forming a well in the wafer, the well being open to the second side;dispensing an epoxy material having a viscosity between 1 cP and 10,000cP onto a sidewall of the well using a needle or syringe in a manner soas to induce a capillary effect that causes the epoxy material to wickdown the sidewall, across a back side of the transducer membrane exposedby the well, and up a second opposing sidewall of the well such that thewell is partially filled substantially without air bubbles; deflectingthe transducer membrane by applying pressurized air from the first sideuntil the transducer membrane achieves an arcuate shape; and curing theepoxy material while the transducer membrane is deflected.
 17. Themethod of claim 16, wherein the deflecting and the curing are performedinside a transducer shaping apparatus.
 18. The method of claim 16,further comprising thinning the wafer from the second side after thecuring of the epoxy material.
 19. The method of claim 16, wherein thedispensing is performed such that a predetermined amount of headspace isreserved in the well.
 20. The method of claim 16, wherein dispensing theepoxy material onto the sidewall includes positioning a tip of theneedle or syringe in physical contact with the sidewall.
 21. The methodof claim 16, wherein dispensing the epoxy material onto the sidewallincludes adjusting a vertical position of a tip of the needle or syringewithin the well.
 22. The method of claim 16, wherein deflecting thetransducer membrane occurs after dispensing the epoxy material such thatthe well is partially filled.